Is expiation obligatory for breaking covenants and vows made while suffering from obsessive-compulsive disorder, or is there no accountability for the one afflicted with OCD?

A vow or an oath is only binding if uttered verbally. Whatever is a mere thought does not count. And whatever you uttered by way of a vow or an oath while under the influence of obsessive thoughts (waswasah) does not count against you, because you are in the position of one who is coerced.